In power line communications, power lines are used as a transmission medium. Power Line Carrier modems transmit high frequency signals over a power line and the signals may be narrow-band (perhaps a few kHz wide) or up to broad-band (many MHz wide). These devices are usually capacitively or inductively coupled onto the power line so as to minimize or eliminate any 50/60 Hz or other high voltage low frequency signals from being transferred into the modems. It is a common problem, however, that most PLC modem transmitters do not properly match the high-frequency characteristics of the power line and hence, transmit with less than optimal efficiency and transmit in frequency ranges where little power is actually passed onto the power lines. Impedance mismatches can also affect the output amplifier waveform and may introduce undesired distortion, intermodulation products and other undesirable characteristics. Also, PLC modems do not possess any capability of sensing subtle changes in power line characteristics as may be noted by measurement of S-parameters for the power lines. What is needed is an improved PLC modem which addresses these shortcomings.